[ticket/12963] Fix the list of migrations in database_update.php

Without this patch the finder grab all the class available in the ext
folder and not only the migrations. This change is backported for the one
done before to the cli tool db:migrate. (see the commit
3420f8f3201ac337434f73ee00bda6df7b378212)

PHPBB3-12963
[ticket/12963] Don't use static var in \extension\base\get_migration_file_list

The static var was global to all instance of \phpbb\base and so if two
different instances (for two different extensions) were created by the
same script they shared the same migrations list.

PHPBB3-12963
[ticket/12963] Load extensions migrations from /migration

PHPBB3-12963
[ticket/12963] Add unit tests

PHPBB3-12963
[ticket/13036] Make the reference type configurable when generating a route

PHPBB3-13036
[ticket/13036] Add unit tests

PHPBB3-13036
[ticket/12963] Edit deprecation message

PHPBB3-12963
[ticket/13036] Complete tests

PHPBB3-13036
[ticket/13069] Fix timezone location filtering.

$timezone contains the original jQuery object, therefore the subsequent
removal of the optgroup children while filtering has no effect on the
$replacement object - the one that's now visible to the user. We'll simplify
and fix this by injecting the content of the copy instead of going through the
trouble of cloning it.

PHPBB3-13069
Merge pull request #2959 from prototech/ticket/13069

[ticket/13069] Fix timezone location filtering.
Merge pull request #2932 from Nicofuma/ticket/12963

[ticket/12963] Load extensions migrations from /migration
Merge pull request #2922 from Nicofuma/ticket/13036

[ticket/13036] Make the reference type configurable when generating a route
[ticket/12858] Generate timezone selects with template loop

PHPBB3-12858
[ticket/12858] Use UTC for time info in footer and hide offset if it's 0

PHPBB3-12858
[ticket/12858] Remove hardcoded language entries from timezone selects

PHPBB3-12858
[ticket/12858] Fix timezone display on acp users page

PHPBB3-12858
[ticket/12858] Fix timezone select display in subsilver2

PHPBB3-12858
[ticket/12858] Rename tz_ prefixed block variables to timezone_ prefix

PHPBB3-12858